In Chicago, we have HDTV channel (true as in where on the spectrum) on 43 and 45. The channel 43 has SIX subchannels. How can this be accomplished with 1 6-mhz width window?
JL
Multicasting and artifacs
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They can fit up to six standard definition compressed digital channels in the 6Mhz bandwidth, each uses about 3Mbit/sec out of the total 19Mbit/sec available from the 6Mhz bandwidth. In my area, a couple channels broadcast 1 HDTV with 1 SD sub-channel. I assume that this reduces the available bitrate of the HDTV channel down to 16Mbit/sec, reducing its quality somewhat - I hate that.
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Mulitcasting and artifacts
This came across my screen recently in regards to PBS multicasting. For a while now folks have been complaining about problems since ABC and NBC started multicasting. The problem is we all seem to have a different experience. I have not noted anything different in either ABC or NBC yet the complaints persist.
>I seem to recall that multicasting was an "either/or" proposition, meaning
>you either provided a full bandwidth HD stream and no subchannels, or you
>provided multiple subchannels and no HD stream. But I'll admit that this
>understanding of multicasting is based more on anecdotal information that
>I've picked up here and there since the initial rollout of HD in 1998. What
>I really want and need is something with a bit more "oomph" behind it that I
>can use in my communication with KETC.
There are no rules on multicasting per se, other than a quid pro quo
made with network broadcasters and the FCC early on that they carry
HD during prime time. PBS stations have no such arrangement and can
do whatever they please since programming decisions are made by the
local station.
A station may carry an HD, an HD/SD, multiple SDs or anything else
their encoder software and the ATSC standard allows them to cram into
19.39 Mbps. The standard precludes nothing. The FCC rules preclude
nothing for public broadcasters.
The quality of the HD encode you see in your home is made up of two
factors: the quality of the encoder at the station and the ability of
your own decoder box to decode. I have seen many boxes over the last
10 years, and full-bandwidth 19.39 HD can look like crap on a decoder
with poorly written or implemented software or hardware, and the SAME
STREAM can look fantastic on a well-designed box.
Please remember that artifacts that you see may well be your own box,
not just what the encoder at the station is doing. It is a problem
which is well known at companies that distribute digital video (of
which mine is a major participant), and provides an endless source of
frustration since getting encoder and decoder manufacturers to
conform to the MPEG-2 standard without adding 'undocumented features'
is like pulling teeth. It is an issue I deal with professionally
every day and it is vexing indeed.
A high-quality encoder (such as the Harris Flexicoder, the Digital
Vision, or the Harmonic) can produce truly beautiful HD down to about
14 Mbps without a problem. That's enough space to include an SD as
well at 4 Mbps. The problem is when a consumer buys a decoder with
software that ASSUMES that an HD is at 18 Mbps (out of 19.39) and
decodes accordingly. It tiles, produces mosquito noise, breaks up on
action scenes, EVEN WHEN THE DECODER AT THE STATION SHOWS EVERYTHING
LOOKS GOOD.
Below 14 Mbps, or if the encoder has older software or is not one of
the brands I listed above, the problem may indeed be the encoder at
the station. Then the problem is a policy and programming decision
to be made by station management. That is when writing a letter will
start to have an effect.
In KETC's case, it sounds like they are the latter: HD below 14 Mbps
with an HD/SD multicast as a station programming decision. Write
often. Call often. Complain vociferously. Become a member and
attend annual station functions and pigeon-hole the General Manager
and complain as a station member. Then they will listen. Public TV
stations multicast because they can and no one complains. Change
that.
>
>I don't know if anyone shares my concern about PBS's multicasting practices,
>but as someone who's wary of HD image quality being progressively
>compromised and diluted over time -- like NTSC before it -- I think PBS is
>establishing a singularly negative HD precedent for broadcasters and other
>program distributors.
One thing you MUST understand is that multicasting as a local
programming decision does NOT come from PBS. The Public Broadcasting
Service is a distribution system ONLY and doesn't set the rules nor
set policy for the public TV stations. Programming decisions are
made at two programming conferences each year where the member
stations (because they are owners of PBS, not affiliates) decide what
to fund and how to schedule programming for transmission over the PBS
distribution system. ALL PROGRAMMING DECISIONS, INCLUDING
MULTICASTING, ARE MADE AT THE LOCAL STATION.
That is why PBS is the Public Broadcasting SERVICE, not the Public
Broadcasting SYSTEM: it is just a distribution service to the
stations not a network making programming decisions.
If you look on the two satellite transponders that transmit PBS DTV
programming to stations, you will find one full-bandwidth ATSC
compressed HD at 19.39 Mbps and another transponder with an SD
4-channel multicast. PBS also transmits about a dozen other program
streams to stations, including PBS You, and east and west coast feeds
of the PBS primary channel, and the PBS C-band feed (the one you see
on DirecTV or Dish if you have no local PBS affiliate). Each program
stream is SD operating at about 8 Mbps. How the stations use those
program streams is up to them, because THEY own PBS, not vice-versa.
If you have complaints about how much HD is being compressed at the
local level, call or write your local PBS station. This has been a
thorn in the sides of us who have worked for the PBS DTV group in the
past: we provide the best HD PBS can provide from the best HD
encoders available, and the stations butcher it as if its just
another program stream.
Really very frustrating for those of us who know what HD looks like
for real when it leaves PBS master control.
Hope this helps,
James Snyder
Senior Video Technician, Ground Network Systems
Intelsat Ltd.
http://www.intelsat.com/
formerly DTV Consultant
DTV Strategic Services Group
Public Broadcasting Service
http://www.pbs.org/
>I seem to recall that multicasting was an "either/or" proposition, meaning
>you either provided a full bandwidth HD stream and no subchannels, or you
>provided multiple subchannels and no HD stream. But I'll admit that this
>understanding of multicasting is based more on anecdotal information that
>I've picked up here and there since the initial rollout of HD in 1998. What
>I really want and need is something with a bit more "oomph" behind it that I
>can use in my communication with KETC.
There are no rules on multicasting per se, other than a quid pro quo
made with network broadcasters and the FCC early on that they carry
HD during prime time. PBS stations have no such arrangement and can
do whatever they please since programming decisions are made by the
local station.
A station may carry an HD, an HD/SD, multiple SDs or anything else
their encoder software and the ATSC standard allows them to cram into
19.39 Mbps. The standard precludes nothing. The FCC rules preclude
nothing for public broadcasters.
The quality of the HD encode you see in your home is made up of two
factors: the quality of the encoder at the station and the ability of
your own decoder box to decode. I have seen many boxes over the last
10 years, and full-bandwidth 19.39 HD can look like crap on a decoder
with poorly written or implemented software or hardware, and the SAME
STREAM can look fantastic on a well-designed box.
Please remember that artifacts that you see may well be your own box,
not just what the encoder at the station is doing. It is a problem
which is well known at companies that distribute digital video (of
which mine is a major participant), and provides an endless source of
frustration since getting encoder and decoder manufacturers to
conform to the MPEG-2 standard without adding 'undocumented features'
is like pulling teeth. It is an issue I deal with professionally
every day and it is vexing indeed.
A high-quality encoder (such as the Harris Flexicoder, the Digital
Vision, or the Harmonic) can produce truly beautiful HD down to about
14 Mbps without a problem. That's enough space to include an SD as
well at 4 Mbps. The problem is when a consumer buys a decoder with
software that ASSUMES that an HD is at 18 Mbps (out of 19.39) and
decodes accordingly. It tiles, produces mosquito noise, breaks up on
action scenes, EVEN WHEN THE DECODER AT THE STATION SHOWS EVERYTHING
LOOKS GOOD.
Below 14 Mbps, or if the encoder has older software or is not one of
the brands I listed above, the problem may indeed be the encoder at
the station. Then the problem is a policy and programming decision
to be made by station management. That is when writing a letter will
start to have an effect.
In KETC's case, it sounds like they are the latter: HD below 14 Mbps
with an HD/SD multicast as a station programming decision. Write
often. Call often. Complain vociferously. Become a member and
attend annual station functions and pigeon-hole the General Manager
and complain as a station member. Then they will listen. Public TV
stations multicast because they can and no one complains. Change
that.
>
>I don't know if anyone shares my concern about PBS's multicasting practices,
>but as someone who's wary of HD image quality being progressively
>compromised and diluted over time -- like NTSC before it -- I think PBS is
>establishing a singularly negative HD precedent for broadcasters and other
>program distributors.
One thing you MUST understand is that multicasting as a local
programming decision does NOT come from PBS. The Public Broadcasting
Service is a distribution system ONLY and doesn't set the rules nor
set policy for the public TV stations. Programming decisions are
made at two programming conferences each year where the member
stations (because they are owners of PBS, not affiliates) decide what
to fund and how to schedule programming for transmission over the PBS
distribution system. ALL PROGRAMMING DECISIONS, INCLUDING
MULTICASTING, ARE MADE AT THE LOCAL STATION.
That is why PBS is the Public Broadcasting SERVICE, not the Public
Broadcasting SYSTEM: it is just a distribution service to the
stations not a network making programming decisions.
If you look on the two satellite transponders that transmit PBS DTV
programming to stations, you will find one full-bandwidth ATSC
compressed HD at 19.39 Mbps and another transponder with an SD
4-channel multicast. PBS also transmits about a dozen other program
streams to stations, including PBS You, and east and west coast feeds
of the PBS primary channel, and the PBS C-band feed (the one you see
on DirecTV or Dish if you have no local PBS affiliate). Each program
stream is SD operating at about 8 Mbps. How the stations use those
program streams is up to them, because THEY own PBS, not vice-versa.
If you have complaints about how much HD is being compressed at the
local level, call or write your local PBS station. This has been a
thorn in the sides of us who have worked for the PBS DTV group in the
past: we provide the best HD PBS can provide from the best HD
encoders available, and the stations butcher it as if its just
another program stream.
Really very frustrating for those of us who know what HD looks like
for real when it leaves PBS master control.
Hope this helps,
James Snyder
Senior Video Technician, Ground Network Systems
Intelsat Ltd.
http://www.intelsat.com/
formerly DTV Consultant
DTV Strategic Services Group
Public Broadcasting Service
http://www.pbs.org/